Rheology Control

DDS-Modified Hydrophobic Fumed Silica: Properties, Applications and Grade Selection Hydrophobic fumed silica is widely used to improve rheology, reinforcement, moisture resistance, and anti-settling performance in industrial formulations. Among different surface treatments, Dimethyldichlorosilane (DDS) modified fumed silica is a popular choice for applications requiring good hydrophobicity and reliable rheological control. What Is DDS-Modified Fumed Silica? DDS-modified fumed silica is produced by surface-treating fumed silica with dimethyldichlorosilane (DDS). The surface treatment reduces the hydrophilic character of the silica particles, improving their compatibility with moisture-sensitive and hydrophobic formulations. Compared with untreated hydrophilic fumed silica, DDS-modified grades generally provide better moisture resistance, dispersion behavior, rheology control, and anti-settling performance in suitable formulations. Key Properties DDS-modified hydrophobic fumed silica can provide several important functions: Hydrophobicity: Helps reduce moisture sensitivity in formulations. Rheology Control: Improves viscosity and thixotropic behavior. Reinforcement: Enhances the mechanical properties of selected polymer and silicone systems. Anti-Settling: Helps maintain stable dispersion of fillers and pigments. Processing Flexibility: Different surface-treatment levels and specific surface areas allow formulators to select a suitable grade. DDS Fumed Silica Grade Selection GESEESIL offers several DDS-modified hydrophobic fumed silica grades with different specific surface areas and carbon contents. Grade Specific Surface Area Carbon Content B210 120 ± 20 m²/g 0.5–1.0% B220 120 ± 20 m²/g 1.0–1.5% B221 120 ± 20 m²/g 1.5–2.0% B230 120 ± 20 m²/g 1.5–2.0% B231 120 ± 20 m²/g 2.0–2.5% In general, grades with higher specific surface area can provide stronger thickening, thixotropic, and reinforcing effects. B230 and B231 are suitable options when higher surface area and stronger rheological performance are required, while B210 and B220 can be considered for applications requiring a lower surface-area grade. B230 and B231 have the same target specific surface area, but B231 has a higher carbon content, providing a different surface-treatment profile for formulation optimization. Common Applications DDS-modified hydrophobic fumed silica is commonly used in: RTV silicone rubber Silicone sealants Adhesives Paints and coatings Electronic encapsulation materials Composites and specialty formulations The optimal grade and dosage depend on the base polymer, formulation composition, processing method, and required viscosity or thixotropy. Choose the Right DDS-Modified Fumed Silica Selecting the right grade is important for achieving the desired balance between hydrophobicity, viscosity, thixotropy, reinforcement, and dispersion. GESEESIL DDS-modified hydrophobic fumed silica is available in multiple grades to meet different formulation requirements. Contact us to discuss your application and find a suitable grade for your formulation.